Can anyone comment if they have combined an emergency blanket with their sleeping bag as an ultralight solution to a warmer but heavier bag? Is it just as effective? If you did, what was the outside temperature, sleeping bag rating and whether you were cold or not.

I have successfully used the AMK Thermal Bivy (not the emergency bivy) instead of a sleeping bag as an ultralight quilt for two people. I previously cut the bivy open to make it into a large quilt, and wore a tee-shirt, lightweight thermal pants and socks for the night, which was spent in a tent, not under a tarp. I was plenty warm overnight and so was my wife - perhaps the trick was snuggling up close! Temperatures went down to about 10C/50F. The bivy weighs 7 oz, so this amounted to a 3.5 oz "sleeping bag" per person for the night. I thought it was a great way to keep pack weight down on summer trips.